1. Field of Invention
This invention relates to a lubricating grease composition having improved resistance to removal by water, improved pumpability over a wide range of ambient temperatures, and the ability to float on water which is specially suitable for lubrication of heavy steel processing equipment.
2. Description of Prior Art
Lubricating greases thickened with a lithium soap of a fatty acid are commonly used in steel mills for the general purpose lubrication of heavy steel processing equipment. Specific improvements in such greases are needed in view of current trends toward more severe operating conditions and better pollution control. Although no doubt many attempts have been made in the past to overcome the difficulties involved in successfully formulating a grease composition which simultaneously possesses (1) resistance to removal by water so that the grease tends to remain on the lubricated bearing, (2) pumpability over a wide range of ambient temperatures, and (3) the ability to float on water to allow the grease, even after severe contamination, to be skimmed from the top of a settling pond as an effective, inexpensive means of water pollution control, none has been successful until the present invention.
The prior art has been aware of the use of polyisobutylene for its adhesive properties. However, the polyisobutylene employed has been one of relative low molecular weight. An example of this grease composition is described in U.S. Pat. No. 3,663,726. The lithium base grease composition in U.S. Pat. No. 3,663,726 contains 3 to 20 percent by weight of a lithium soap thickener, 70 to 96 percent by weight of a hydrocarbon lubricating oil having a viscosity ranging from 40 to 165 SUS at 210.degree. F and 1 to 25 percent by weight of a linear polyisobutylene having a molecular weight of from 5,000 to 20,000 (Staudinger) to obtain lubricating grease having a consistency of about 220 to 430 penetration number as measured by ASTM D-217. This composition has been formulated and evaluated as Example No. 8 in the experimental data herein and does not have the desired properties demonstrated by the grease composition described in this disclosure.